The present invention relates to polyolefin resins containing inorganic fillers and particularly to the method of preparing such filled resins wherein the product so produced has an unexpected reduction in loss of impact strength.
Fillers, such as inorganic metal oxides and carbonates, have long been used as additives to polymer resins to improve certain physical properties, to tailor such resins for particular end use, or to reduce the amount of resin required for a particular fabricated article. Polyolefin resins containing inorganic metal fillers generally have increased stiffness of modulus, improved dimensional stability, increased compressive strength, and improved creep resistance over the unfilled resin. However, other physical properties of polyolefin resins, such as impact strength, are detrimentally affected by the addition of fillers. These property losses are due, at least in part, to the incompatibility between the filler and the base polyolefin resin.
It has been suggested to use coupling or bonding agents in the manufacture of filled polymer resin systems to compatibilize or couple the filler with the base resin. This frequently requires pretreatment of the filler with organic compounds such as organic titanates or silanes followed by blending of the treated filler with the base resin. The effectiveness of these coupling agents in polyolefin resins has been quite limited since the suggested coupling agents do not react to any significant extent with the base polymer resin. Reduction in loss of impact strength, for example, is not obtained.